Production of cobalt strip and the like



United States Patent 3,425,828 PRODUCTION OF COBALT STRIP AND THE LIKEArthur T. Cape, Monterey, Califi, assignor to Coast Metals, Inc., LittleFerry, N.J., a corporation of Delaware No Drawing. Filed Mar. 11, 1966,Ser. No. 533,423 US. (3]. 75-214 4 Claims Int. Cl. B221. 1/00 ABSTRACTOF THE DISCLOSURE The addition of between 2 percent to 4 percent byweight of iron powder to cobalt powder whereby the resulting mechanicalmixture of powders is more readily cold formable than a similar cobaltpowder without the added iron.

This invention relates, in general, to the production of cobalt strip,foil, and the like, but has reference more particularly to theproduction of such strip, foil, and the like, by cold forming.

It has heretofore been proposed, as in the Faulkner Patent No.3,091,022, to provide a cold-formable predominantly cobalt alloy bychanging the crystalline structure of the cobalt, which, at roomtemperature, has an hexagonal close-packed crystal structure, to aface-centered cubic crystalline structure. This is accomplished byincorporating in or adding to the cobalt at least one of the elementscarbon, iron and nickel, in a predetermined amount. Althoughcommercially available cobalt may contain a small amount of nickel,iron, carbon or other impurities which cannot be avoided duringrefinement of the metal, these metals or elements are not present insufficient amounts nor in the proper proportions required to retain aface-centered cubic structure at room temperature.

The predominantly cobalt alloy in the aforesaid Faulkner patent is madeby melting under standard furnacing procedures, preferably by vacuummelting, and the alloy may then be hot-worked, or may be cold-worked bywellknown methods to produce sheet, tubing, wire, strip, etc.

It has also been proposed, as described in an article entitledProperties and Applications of Cobalt Strip, 'by Fraser, Evans andMackiw, on pages 80-84 of the July 1964 issue of Metal Progress, toproduce ductile cobalt strip by compacting cobalt powder of high purity(99.92%). The powder is rolled into a continuous coil of green stripwhich is then sintered and hot rolled, and the densified cobalt strip iscold-rolled to the desired gauge or thickness. The hot rolling isperformed at 1750 F. In the cold rolling, the strip is cold rolled tonearly the density of solid cobalt and finally, it is annealed in bellfurnaces at temperatures up to 1700 F. for 1 hour. The finished cobaltstrip consists of combined hexagonal closepacked and face-centered cubicstructures, the mixture of these depending on the actual annealingtemperature.

I have found that I can produce a cold-formable predominantly cobaltproduct without changing the hexagonal close-packed crystal structure ofthe cobalt, and with a minimum of annealing of the cold-formed productby utilizing, to form the product, a mixture of cobalt powder and ironpowder, with the iron powder comprising from about 2% to about 4% byWeight of the mixture.

In general, the powders in the mixture should be of a size of minus 150mesh, but preferably not smaller than 500 mesh.

The mixture of powders is compacted by cold pressure or by cold rollinginto a flat plate or sheet, or into a continuous coil, which is thensintered, if necessary, to agglomerate the particles of powder into aworkable mass.

After sintering, the cold pressing or cold-rolling is continued untilstrip or foil of the desired gauge or thickness is obtained.

Hot rolling may be used to increase the readiness with which the stripis reduced to smaller gauges.

The strip or foil may be used as such, or may be formed into tubing,wire, etc.

The maximum effect, for the purposes of this invention, is obtained byusing from about 3% to about 3 /2% by weight of iron powder in themixture.

Studies using X-ray diffraction show that the structure of both thesintered material as well as the finished strip or coil isoverwhelmingly hexagonal close-packed, and no evidence of aface-centered cubic structure has been found.

Microscopic examination establishes that there is little or no solidsolution of the iron in the cobalt, and that in the finished strip orfoil, the iron is found in long stringers and not in solid solution inthe crystals of cobalt. The formation of a face-centered cubiccrystalline structure, such as is found in the product of the Faulknerpatent and in the product of the Metal Progress article referred toabove, requires the solid solubility of the iron in the cobalt inFulkners invention, or repeated annealing of the cobalt strip in theMetal Progress method.

I have thus produced a cobalt strip or foil by a coldforming method,which strip or foil is characterized by the essentially hexagonalclosed-packed crystal structure of the cobalt, and by the presence of asmall amount of iron in the form of long stringers, and substantiallynone of which is in solid solution in the cobalt.

Having thus described my invention, I claim:

1. The method of producing a cold-formable predominantly cobalt producthaving an hexagonal close-packed crystal structure of the cobalt whichcomprises: providing a mechanical mixture consisting of cobalt powderand iron powder, with the iron powder forming from about 2% to about 4%by weight of the mixture, both powders being of a size of minus 150 meshbut not smaller than about 500 mesh, and then compacting the mixtureinto strip or foil, whereby the addition of the iron powder to themixture permits compacting with a minimum of annealing.

2. The method as recited in claim 1 wherein the mixture of powders iscompacted by cold pressure into a flat plate, sheet or continuous coil.

3. The method, as recited in claim 2, wherein hot rolling is used toincrease the speed with which the strip or foil is reduced to smallergauges, but without annealing of the strip or foil.

4. The method, as recited in claim 1, wherein the iron powder forms fromabout 3% to about 3.5% by weight of the mixture.

References Cited UNITED STATES PATENTS 3,091,022 5/1963 Faulkner 2919l.2

3,270,409 9/ 1966 Grant -226 3,330,654 7/1967 Sweet 752l4 X FOREIGNPATENTS 1,004,457 3/ 1957 Germany.

OTHER REFERENCES Metal Industry, June 11, 1948, p. 487.

Metal Progress, July 1964, pp. -82, 84.

Fundamental IPrinciples of Powder Metallurgy, Tones, 1960, p. 364-365.

Treatise on Powder Metallurgy, Goetzel, vol. I, pp. 3, 4, 524-525.

CARL D. QUARFORTH, Primary Examiner. A. I. STEINER, Assistant Examiner.

US. Cl. X.R. 75200, 226; 29--182

